There are content inset problems if a ASViewController is initialized with a root node (e.g a ASCollectionNode subclass) that has usesImplicitHierarchyManagement set to YES. The reason for that is that the subviews (e.g. the UICollectionView) of the ASViewController root node get's added to the view hierarchy in measureWithSizeRange: in ASDisplayNode. measureWithSizeRange: of the root node is called in -viewWillLayoutSubviews in ASViewController. That is too late, so UIKit does not apply the automatic content inset to the UICollectionView anymore.
ASViewController currently cannot be subclassed in Swift, as the original call to `[super init]` directs to calling the designated initializer of UIViewController `[self initWithNibName:bundle:]`. Because of Swift's initializer inheritance behavior, this designated initializer will not implicitly be available on the subclassed ASViewController without some extra boilerplate. Adding an explicit call to the designated initializer fixes this issue.
This provides internal features on _ASAsyncTransaction and ASDisplayNode to facilitate
implementing public API that allows clients to choose if they would prefer to block
on the completion of unfinished rendering, rather than allow a placeholder state to
become visible.
The internal features are:
-[_ASAsyncTransaction waitUntilComplete]
-[ASDisplayNode recursivelyEnsureDisplay]
Also provided are two such implementations:
-[ASCellNode setNeverShowPlaceholders:], which integrates with both Tables and Collections
-[ASViewController setNeverShowPlaceholders:], which should work with Nav and Tab controllers.
Lastly, on ASDisplayNode, a new property .shouldBypassEnsureDisplay allows individual node types
to exempt themselves from blocking the main thread on their display.
By implementing the feature at the ASCellNode level rather than ASTableView & ASCollectionView,
developers can retain fine-grained control on display characteristics. For example, certain
cell types may be appropriate to display to the user with placeholders, whereas others may not.
Follow-up work will include unit tests, revisiting names, and the header locations of definitions.
